The present invention relates to a power take-off (PTO) mounting arrangement and, more particularly, to a power take-off shaft stabilizer unit.
Because of superior operator visibility, maneuverability and relative stability, vehicles having front mounted (FM) mowers have become increasingly popular for lawn care operations. The front mount mower is conventionally configured a a front wheel drive, rear wheel steer vehicle which includes a front hitch for the attachment of implements, such as a mower deck or snowblower. With this configuration, in order to deliver power to the attached implement, it is known to equip the front mount vehicle with a PTO system for selectively communicating between the engine and the front mounted implement.
Because a front mounted vehicle has a relatively short length and low ground clearance, many conventional PTO systems are ill-suited for the incorporation therein. Further, the use of diesel and other engines which exhibit a high torque displacement and vibration cause problems which must be considered when selecting a suitable PTO system. Diesel and similar engines, due to the higher torque displacement and vibration require that allowances be made for the vibration between the engine crankshaft and the PTO shaft. Specifically, the belts conventionally utilized to transfer power from the engine to the PTO, in order to operate efficiently and to achieve long life, must maintain a certain tension between the pulleys on the engine crankshaft and the PTO shaft. Additionally, if the PTO shaft is positioned by a bracket attached to the engine rather than mounted on the vehicle frame, accommodation must be made for maintaining a relatively constant position between the PTO shaft relative to the bracket.
As with all PTO systems, substantial counterloading of the engine crankshaft or crankshaft bearings, which could precipitate engine crankshaft misalignment or premature cam shaft bearing failure, must be avoided. It is known that a PTO system driven off the crankshaft from an engine torque shaft may produce a counter resistance to engine torque deflection where the PTO system is hard mounted to the vehicle frame and is driven from the torque shaft from a fixed length medium such as a continuous belt. The counter resistance caused by the belt during engine torque displacement imparts a crankshaft torque about the crankshaft bearing which may result in engine misalignment.
It is equally important that the PTO system not unduly load the torque shaft between the engine and the transaxle when the PTO shaft is connected to the engine crankshaft at the location between the engine crankshaft and the transaxle.
One prior solution to the above problems encountered when mounting the PTO shaft to the engine and connecting the engine drive shaft and the PTO shaft at a position between the engine and the transaxle when the PTO shaft is mounted to the engine frame is disclosed in U.S. Pat. No. 4,640,378 issued Feb. 3, 1987 and commonly owned with the present application. In that patent, a key was provided in a slot of the bearing quill, however, the various components required high dimensional accurancy, because if they were to be loosely fit, vibration from the belts would cause considerable noise and wear. With wear, the noise increases, thus, this particular solution proved unacceptable when the high dimensional accuracy was not maintained.
An additional problem encountered with the above mentioned patent was that of changing belts. With the structure disclosed in the above patent, it was necessary to disassemble the engine crankshaft in order to remove the old belts and replace them with new belts. This complicated, time consuming, operation proved unacceptable to commercial users of FM vehicles.
Thus, there is a need for a power take-off shaft stabilizer unit which insures that the proper belt tension be constantly maintained between the engine crankshaft and the PTO shaft; which provides for rapid disassembly and replacement of worn belts with new belts; and, which eliminate the excessive noise and other problems associated with the prior systems.